Method of reconditioning rock drill bits



Jan. 6, 1942.

y F. MccARTHY,-JR A 2,268,715

METHOD 0F REGONDITIONING ROCK DRILL BITS Filed June 24, 1939 2 sheets-sheet 2 JAMES vF. uay-cARTHY, JR.

:inventor Gttorneg Patented Jan. 6, 1942 METHQDOF RECONDITIONING ROCK DRILL l BITS James F. McCarthy, Jr., Wallace, Idaho Application .lime 24., 1939, Serial No. 280,981 6 Claims. i(Cl. VG+-108) It is therefore a purpose and object-of my present invention to recondition used bits without the necessity of expensive forging methods required for upsetting and expanding the width of the points in order to meet a standard or upon re-gauging the tool will have the same Drilling bits, especially those used inconnecl tion with modern high-powered heavy duty drilling machines, have certain characteristics that are maintained by substantially vall of the drill bit manufacturers. 'Ihe usual drill bit is provided with either two, four or six points. VThese points or cutting edges radiate from a ycommon center and have clearance channels or,g'rooves to permit the cuttings to freely pass rearwardly as the drilling work progresses. Each of these tools may also be provided with an axially dis-Y posed water hole, usually slightly enlarged at its end adjacent the points or cutters. Such 4a drill bit is also provided with a short shank having interior threads by means of which it ismounted to the end of a drill rod.

In drilling, especially in hard rock, the drill is started into the face of the rock and driven forward through a rapid succession of hammer blows applied by the drilling machine. Water or air, or a combination of both, is supplied which passes through the drill rod and through the bit and assists in removing or washing the cuttings from the face of the bit. The bit is rotated so that the points are constantly presented in a new position against the bottom of the hole, and the drilling is continued so long as the -bit maintains the required sharpness or ability to cut and fracture the rock against which it is worked. Usually a bit is capable of drilling la hole one or more feet in depth, whereupon it has to be removed and a sharp bit adjusted to the end of the drill rod to continue the work.

Since the recent adoption in mining and vother rock drilling of the detachable type of bit, it has been the practice in the iield to either grind new points -or cutters on the bit and re-gauge the bit for drilling a hole of smaller diameter, to die-forge the bit back to its original size, or to discard the bit after a single use. After one or two such sharpening processes the bit has to be discarded, since it no Alonger permits a gauge within the range demanded.

diametrical dimensions originally provided in the unused tool and so that it will have all of the rest of the original characteristics of such a tool,

It is a further purpose, through the method I have adopted, to make it possible to renew a tool a number of times to its original' gauge and subsequently recondition the tool for lesser gauges in succession, `the vreconditioning 4process continuing until there is insuflicient metal left out of which to form new points.

It is 'a still further object of the invention to materailly reduce the cost of drilling by reducing the .cost per use of each bit and by increasing the number of times a bit may be used.

In order that my improved process may readily be understood I havedisclosed, in the accompanying drawings, so much of a detachable type'of bit, with several views thereof, as best to illustrate the principles involved in reconditioning such a bit for continued use.

In Figure 1 I have illustrated in perspective standard four-point detachable bit. f

Figure 2 is a perspective View of a detachable type four-point bit, disclosing the wear imposed upon a bit during a single use or operation.

Figure 3 is a partial cross section through a new bit, showing the points, the gauge and, in dotted lines, the approximate line of wear when the points are dulled through use.

Figure 4 illustrates a partial cross section through a bit on the line of one of the vpoints of a Worn bit and showing in dotted lines the required change inline and form for a recon l ditioned bit.

Figure 5 isa partial cross section through one of the points of a bit after reconditioning. Figure 6 is aside View of a standard type detachable bit, sho-wing the position in which it is applied to a milling cutter used in connection with my process and in which the bit is supported and rotated to engagement with lthe mill.

Figure '7 is a partial view of the lower section of a milling cutter used in reconditioning bits, in which the shaded portion illustrates the area of the bit contacted by the milling cutter during the application of the bit to the cutter.

Figure 8 is an edge view of the face of the milling cutter and a perspective view of a bit in position to be reconditioned.

It is the practice in some mining fields to make a starting hole at 21/8 inch diameter. Whenk the bit has become dulled it has lost its original gauge and is somewhat less at the point where the tool becomes dulled than at the start, effecting a tapered hole. succeeding sharp bit is then used having a gauging diameter usually V8 of an inch less than the first bit. Succeeding drills drop down 1/8 of an inch each time a new bit is used, and usually a finished hole will be 1% inches in diameter. This requires at least four different drills, having gauge diameters of 2% inches, 2 inches, 1% inches and 1% inches, and the hole, as a result of this operation and due to the wear of the tool as it progresses into the rock, is tapered from 21/8 inches to 1% inches.

In order to maintain the hole of equal diameter throughout, resort would have to be made to reaming each section of hole as it was made, which operation would materially add to the expense of drilling and would also increase the diiiiculties encountered due to the fact that the tool would be much more inclined to jam, requiring loss of time for the power unit as well as the time of labor involved in releasing the tool and re-reaming in order to continue. Standard practice involves the use of powerful equipment and of the best bits that it is possible to buy in order to secure the economy necessary to keep the cost within the range permitted with relation to the value of the 'ore being worked upon.

Percussion type drilling machines, which include jack hammers, drifters and automatically rotated stope hammers, deliver a rapid succession of blows upon the end of the drill rod to which the. detachable bit is secured, and the points or cutters are affected or dulled in proportion to the work performed `upon the rock or other drilling surface. The exact centerof the bit has little or no travel as a bit rotates during its operation. 'I'he cutting edges on the peripheries or outside of the bit travel the maximum distance, or a distance equal to the circumference of the circle of the bore. Thus in a 21/8 inch bit the outer edge of the cutting face or point in one revolution of the bit will have traveled slightly more than 6% inches, a point intermediate between the center and the extreme outer edge of the cutter will travel approximately 3% inches,

To extend the work a I future use at itsoriginal gauge. In the past the manufacturers of drill bits have made grinders available for use in the field, which grinders are intended to recondition the bits after being worn by grinding new cutting faces or points to the bits. This process, while slow and time-consuming and materially affecting the cost of the reconditioned bit, requires that the bit when reconditioned must be of a reduced gauge, and while it is possible to grind a bit several times, each with a succeeding lesser gauge, the cost of such an operation has been found by most operators to be prohibitive. Another alternative would be to re-forge the bit, and in this operation the expense involved is so great that until recently operatorshave relied almost entirely upon replacing a worn bit with a new bit upon one to two grindings.

Through the method that I have adopted I have discovered an easy and inexpensive way of renewing a bit several times to its original gauge, several times to the next reduced size and in succeeding operations to further reductions, until all the stock or bit material has been used to the point where it is no longer practical to continue to resharpen it. The increase in use by my method has resulted in approximately 100% increased use.

My method involves the use of a rapidly revolving double-angle milling tool wheel. The face of the tool is formed of a double-angle to act in the clearance groove of the bit and along the sides of the cutters or points to re-establish the groove and to form the points by a succession of operations. This latter action involves a swaging of the metal to produce a movement or flow of the material of the bit acted upon to extend the cutting edge outwardly in a singlek operation.

- The milling wheel is substantially a combination of miller and swager. The teeth need not be of extreme sharpness, and it has been found through extensive practice that dull teeth or no teeth at all on the face of the miller will produce the desired result.

Detachable bits II, as shown, have a plurality of cutting vedges 8 and adjacent sloping gauge faces I diametrical with the center axis of the.

bit. The bit I I is heated before the recondition- Y ing operation takes place to approximately forgand the cutter edge at the center hole of the bit i will only travel slightly more than 1 inch in one revolution. The result is that there is but little wear at the inner end of each point or cutter and that the wear increases in proportion to the increase in diameter or distance over which the cutter travels. Hence, anew bit will start to wear progressively toward the outer end of the cutter, resulting in a tapered, flattened area gradually increasing in width from the water hole to the outside end of the cutter. The point of the cutter will be so considerably reduced that the original gauge of the tool is entirely lost, and the hole will be gradually reduced in diameter to effect a tapered bore.

I have endeavored to illustrate herein the problem involved in reconditioning a drill bit for ing temperature. It may be applied to the milling unit I0 by being mounted upon a pivoted bit support, movement of which causes the bit to travel in an arc. The radial center of the arc is to one side and below the miller at point I2.

Through leverage action the bit II is brought forcefully into` engagement with the miller IU. The miller revolves downwardly toward the bit, but the iirstengagement is applied to the heel or bottom I3 of the clearance groove 9 and to the lower facesof the beveled points or cutters. This action causes the metal contacted on the bit to be milled in part aswell as drifted or swaged outwardly to the limits of the cutting edges. Continued application cuts away and removes enough metal to reform thevclearance groove 9, and the action of the outer edges ofthe teeth or milling cutters brings about a swaging action outwardlyube ready for subsequent useand fit to drilling.

performances equal with the original bits. The

cost of the operation is so low that it is possible, through the method herein set forth, to recondition bits at a cost that will materially reduce an operators expenses.

Applying the above to the drawings, I have shown in Figure 1 a new unused bit of a design now standardized, and for a comparison, in Figure 2 I have indicated the approximate condition of a bit after a single use. This bit, to be renewed to its original dimensions, requires new cutting edges or points 8 that shall extend from the center outwardly to a point where gauging is possible at the original size.

In Figure 3, also for illustration, I have shown a partial cross section through a bit, showing the original cutting edge 8 in solid line and in dotted lines the limit of wear of a used bit in which gauge loss, indicated at A, is quite apparent and quite considerable.

In Figure 4 I have indicated the worn bit through one of the cutters, and in dotted line I have indicated the shape of the cutter upon renewal. It is to be noted that the area C, above the dotted line, represents the material removed from the Worn bit in order to recondition this bit, and that the area D on the outer end of the point is re-established by the swaging action aiTorded by applying the heated dulled bit to the miller, in the manner herein described. In this case it has been necessary to swage or extend the points a distance indicated by B in this ure, which represents the same amount of extension as shown as a loss in Figure 3 at A. Thus, when the reconditioning of the bit is completed, it has re-assumed its normal original width and is of standard gauge, and through wear and the reconditioning operation has lost material in height only to the extent indicated in the area E as shown in Figure 5. Successive applications of the method, therefore, cause a reduction in height but in no manner affect its further use under the original conditions of the tool.

The miller I is formed with a double angle face having milling teeth so that the action of cutting or forming the clearance groove at a new depth to permit establishing a new edge for the cutters will cause a combination milling and swaging action upon the drill points 8, effecting a drift of material outward while the cutting edges of the points are being re-established. The metal thus moved or flowed outward is more than suicient to re-establish the original gauge of the tool. Re-gauging is performed in a subsequent operation by applying the tool at the proper angle to .eiect a new gauge having a diametrical center coinciding with the axial center of the bit.

As a further means of illustration I have shown in Figure '7 a shaded area as I4 to indicate the area of the bit engaged by the miller in a single. operation. It must be remembered that the miller acts upon the clearance groove of the bit and upon one side each of two adjacent cutters or points. When this first operation is effected the bit is rotated a one-quarter turn to engage a new groove and new points, and subsequent operations involve again turning the bit a one-quarter turn until all the grooves and point faces have been surfaced and swaged.

Because of the double angle shape of the miller the cutting teeth at the bottom of the V will have a decided cutting action, but since the contacted edge of the bit at the point in the operation when the new cutting edges of the points are being formed is on a decided angle as I5, the

action of the miller has changed from one having a cutting eiect to one where a drifting or swaging of the metal is effected to widen or expand the cutting points 8. To increase the swaging action or that of moving the metal outward to re-establish gauge, the individual miller elements or cutter teeth I'I may be disposed at an angle to the axial center of the wheel. In other words, the sides of the cutters may recede from the nose I6 to elect a plowing action that further enhances the swaging or movement of metal outwardly during the initial action of re-forming or re-establishing a clearance groove.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The method of reconditioning a worn rock drill bit having radial teeth, which comprises heating the bit, presenting adjacent faces of the teeth to a rotating double milling cutter operating outwardly from the center of the bit, urging the heated bit against said rotating cutter suflciently to cause the milling operation to swage the indexed teeth radially outward upon the bit, serially indexing the bit in accordance with the teeth thereon and milling as aforesaid, next cutting the milled and swaged bit to guage diameter, and nally tempering the bit.

2. The method of reconditioning a worn rock drill bit having radial teeth, which comprises heating the bit, presenting adjacent faces of the teeth to a rotating double milling cutter operating outwardly from the center of the bit, urging the heated bit against said rotating cutter sufficiently to cause the milling operation to swage the indexed teeth radially outward upon the bit, serially indexing the bit in accordance with the teeth thereon and milling as aforesaid, and next cutting the milled and swaged bit to gauge diameter.

3. The method of reconditioning a worn rock drill bit having radial teeth, which comprises heating vthe bit, presenting adjacent faces of the teeth to a rotating double milling cutter l operating outwardly from the center of the bit,

urging the heated bit against said rotating cutter sufficiently to cause the milling operation to swage the indexed teeth radially outward upon the bit, serially indexing the bit in accordance with the teeth thereon and milling as aforesaid.

4. The method of reconditioning a worn rock drill bit, which comprises heating the bit, milling the heated bit to form radial teeth, simultaneously by the foregoing step swaging the teeth radially outward upon the bit by causing the milling cutter to operate outwardly from the center of the bit, next cutting the milled and swaged bit to gauge diameter, and nally tempering the bit.

5. The method of reconditioning a worn rock drill bit, which comprises heating the bit, milling the heated bit to form radial teeth, simultaneously by the foregoing step swaging the teeth radially outward upon the bit by causing the milling cutter to operate outwardly from the center of the bit, and next cutting the milled and swaged bit to gauge diameter.

6. The method of reconditioning a worn rock drill bit, which comprises heating the bit, milling the heated bit to form radial teeth, and simultaneously by the foregoing st ep swaging the teeth radially outward upon the bit by causing the `milling cutter to operate outwardly from the center of the bit.

JAMES F. McCARTI-IY, JR. 

